1. Field of the Invention
This invention relates to a semiconductor memory device and a method of controlling the semiconductor memory device. For example, this invention relates to a method of controlling the filter length of a noise filter for removing noise.
2. Description of the Related Art
In recent years, semiconductor memory devices have been made faster remarkably and have made surprising progress in multi-bit design. With the faster operation and multi-bit design, a noise problem has occurred notably. A method of coping with the noise problem has been disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. H07-029377. With the method, a noise filter is provided in an input circuit.
The magnitude of noise is not always constant. Accordingly, with a conventional configuration, the noise removing capability of the noise filter was sometimes insufficient. Moreover, increasing the filter length of the noise filter to improve the noise removing capability makes the filter length unnecessarily great, which causes the problem of decreasing the operating speed.